Field of the Invention
The present invention relates to orthodontic brackets and, specifically an orthodontic bracket wherein an orthodontic wire is held in an open channel or slot which receives an orthodontic wire without means of any type of applied ligature or any type of moving cover. More particularly, the present invention provides a static self-ligating orthodontic bracket.
Description of the Related Art
Orthodontic brackets are well known in prior art. Brackets are glued or cemented to the surface of teeth, or attached to metal bands cemented to a tooth and provide a means for a wire to be attached to a tooth. The wire applies force to the bracket which transmits it to the tooth to move the tooth in the desired manner. A bracket can also provide a slot for a wire to fit in and provide a guide to slide a tooth along a wire by means of force applied by various types of springs, elastics, or other devices to apply force to a bracket and subsequently transmitted to the tooth.
Existing bracket designs require a movable component of the bracket or an externally applied device known as a ligature to prevent the wire from becoming dislodged from the slot during orthodontic treatment. Another design known as a Begg bracket, uses a metal pin fitted into a slot to hold the wire in place. There are many variations on these types all of which require ligatures, pins, or movable components to secure an orthodontic wire into the bracket slot. Brackets which do not require an externally applied component such as a ligature to hold an orthodontic wire in place in the slot, are generally known as self ligating brackets.
Existing designs have a number of problems which hinder efficient orthodontic treatment. The movable component of self ligating brackets can become damaged through normal use in the oral environment, or through abuse by the patient. If the movable component is damaged the bracket may be rendered unusable and require replacement requiring additional clinical treatment time, discomfort to the patient, extension of treatment time, and additional expense. Ligatures require time to apply to each individual bracket, and in the case of esthetic brackets manufactured from transparent or tooth colored materials ligatures stained from various foods in the oral environment can be unsightly leading to patient dissatisfaction.
Orthodontic brackets represent a principal component of all corrective orthodontic treatments devoted to improving a patient's occlusion. In conventional orthodontic treatments, an orthodontist or an assistant affixes brackets to the patient's teeth and engages an archwire into a slot of each bracket. The archwire applies corrective forces that cause the teeth to move into correct positions. Traditional ligatures, such as small elastomeric O-rings or fine metal wires, are employed to retain the archwire within each bracket slot. Due to difficulties encountered in applying an individual ligature to each bracket, self-ligating orthodontic brackets have been developed that eliminate the need for ligatures by relying on a movable portion or member, such as a latch or slide, for retaining the archwire within the bracket slot.
While self-ligating brackets have been generally successful, manufacturers of such brackets continually strive to improve the aesthetics associated with self-ligating brackets, the use and functionality of self-ligating brackets, and the costs and manufacturability of self-ligating brackets.
Orthodontic brackets attached to teeth engage an archwire that exerts forces upon them to move the teeth. Such brackets typically include an archwire slot for reception of the archwire. An archwire slot can have any desired cross-sectional configuration or size to match the size and shape requirements of the archwire, or archwires, that are to be engaged within the slot.
Orthodontic brackets today are typically bonded to a tooth with the archwire slot oriented parallel to the occlusal plane. However, the slot can also be angularly oriented across the bracket when desired.
Most brackets in use today include cleat extensions referred to as tie wings or lugs. they project upwardly and downwardly in pairs at the top and bottom of the installed bracket, respectively. These extensions conventionally permit the archwire to be held within the archwire slot of the bracket by means of a ligature, twisted wire (ligature) or an elastomer O-ring.
Numerous attempts have been made to design brackets that are self-ligating. For example, one such design discloses a slidable closure that engages the front of the archwire. The closure is recessed from the front or anterior surfaces of the disclosed bracket. The fact that such recessed sliding closures require the archwire also to be recessed within the archwire slot before the closure can be moved over the archwire makes it very difficult for the user to visually confirm that the archwire is properly seated within the archwire slot to facilitate closing of the slidable cover.
When using a conventional bracket and tying wires, proper seating of the archwire can be confirmed by visually noting that the anterior surface of the archwire is flush with the anterior surface of the bracket. It is desirable that a self-locking bracket provide similar visual reference capabilities to the user. This cannot be attained where no anterior surface of the bracket is available for visually referencing the position of an archwire within the archwire slot of the bracket.
A self-ligating bracket designed to mount an archwire flush with an anterior surface of an orthodontic bracket to facilitate visual positioning of the archwire during orthodontic treatment is also known. Such bracket disclosures utilize a ligating slide or closure that is permanently retained on the bracket during use, whether the closure is left in an open or closed condition, which guards against accidental release of the closure while the bracket is worn on a tooth.
Most importantly, the closure was designed to leave the usual tying extensions that protrude from the top and bottom of the bracket fully accessible to other orthodontic attachments for the application of torsional forces to the teeth. The exposed tying lugs remain always available for repositioning of the bracket and tooth by use of tying wires or other conventional attachment systems. One achievement of this bracket is the provision of a ligating slide within a bracket that maintains the normal features of protruding tie wings or lugs required by the profession.
The previous bracket embodiments also include a closure in the form of a ligating slide that can complete a continuous tube surrounding the archwire when the closure is in a closed position. This can be effectively achieved in a Siamese or twin bracket configuration without covering or interfering with projecting extensions on the bracket.
Another previous self-ligating orthodontic bracket discloses a locking slide member that is flat and guided by upright slots formed along both sides of the bracket and spanning the archwire slot. A resilient member or detent is provided to retain the slide member in either the open or closed position. No tie wings or lugs are included in the illustrated bracket forms.
Miniaturization of orthodontic brackets is extremely important today in view of the development of modern high-technology archwires. Patients desire small brackets to reduce the visual impact of the brackets while they are being worn. Orthodontists desire smaller brackets in order to more effectively use the biasing forces available in the high technology archwires, it being recognized that the force applied to a bracket by the archwire is decreased with increasing bracket spacing between teeth.
One drawback to miniaturization of the brackets shown in earlier patents is the fact that most of the embodiments wrap the cover over the sides of the bracket to engage grooves posterior to the archwire slot across the bracket. The width of the sliding cover therefore increases the total width of the bracket beyond that which is necessary due to the strength properties of the bracket itself. It is subject to tooth contact due to normal occlusion clearances in the mouth and subsequent failure or damage from the opposing dentition or food.
While the some known methods show a flat cover sliding within the lateral confines of a bracket, the guiding arrangement for the cover includes slots at both the superior and inferior sides of the archwire slot, thereby obscuring visual access to the critical corners of the archwire slots at the side edges of the bracket. Without this visual access being clear, one installing an archwire within a bracket cannot be certain as to proper seating of an archwire within the archwire slot before the slide cover is moved to a closed position. A wire not properly seated in the slot can cause damage to the cover mechanism and require replacement of the bracket interfering with treatment.
Referring to FIG. 1A, shown is a prior art self-ligating orthodontic bracket with the cover shown in a closed position with an archwire held within the bracket. Also, shown in FIG. 1B is the prior art self-ligating orthodontic bracket of FIG. 1A with the cover shown in the open position. The general concepts of the invention can best be understood from a study of the first embodiment of the assembled orthodontic bracket. This form of the bracket includes a movable closure separately shown in FIGS. 1A and 1B. The illustrated bracket, identified generally by the numeral 1, includes a pad 10 having a posterior surface 11 adapted to be bonded directly to a tooth. Pad 10 can be constructed integrally with the bracket 1 or can be a separate component added to it during assembly. The bracket 1 as shown in the drawings is a “Siamese” or pad 10. Tie wings 2 project anteriorly from the bracket 1. Each tie wing 2 two opposed extensions that project outwardly from bracket 1 between transversely spaced side surfaces.
At a minimum, each tie wing 2 includes an outer side surface. In addition, the tie wing configurations shown in the drawings further include inwardly facing side surfaces. The bracket 1 also includes first anterior surfaces 3 across the front of each first tie wing extension. The exposed anterior surfaces 3 extend across the full width of the bracket 1 and tie wing extensions.
Lower planar anterior surfaces lead to opposite sides of a transverse archwire slot generally designated by the numeral 20. The archwire slot 20 spans the full width of the bracket 1, where it opens across the bracket side surfaces. The space along archwire slot 20 between the tie wings 2 can be open, but is preferably enclosed by bracket walls joining the tie wings. This provides a supporting enclosure for an archwire 4 across the hill width of the bracket 1.
The archwire slot includes opposed and spaced side slot surfaces 5 and 6, plus an interconnecting anterior base 7. As can be seen in FIGS. 1A and 1B, the intersections of the side slot surfaces 5, 6 and anterior base 7 with the outer side surfaces of bracket 1 may be rounded or radiused. This provides a smooth edge for engagement by an archwire located within the archwire slot 20 and eliminates high stress and pressure on the archwire surfaces in contact with the ends of the archwire slot. It further facilitates motion between the bracket and archwire as tooth movement occurs in the mouth of a patient.
Side slot surface 5 forms a first transverse anterior corner with the archwire slot 20 where it intersects the anterior surface 3 of the first tie wing extensions. Side slot surface 6 similarly forms a second transverse anterior corner with the archwire slot 20 where it intersects the anterior surface of the second tie wing extensions. It is important to note that the second corner is continuous or coextensive across the full width of bracket 1 between the side surfaces. The anterior surface 3 across the first tie wing extension is free of any projections or closure guides. Thus, a clinician observing the installed bracket on a tooth has an unobstructed view of the open archwire slot 20 from its one side to guide him or her in proper bracket and archwire positioning procedures.
The slot surfaces 5, 6 and 7 are sized and configured in a manner complementary to the size and shape requirements of an archwire (or archwires) adapted to be received within the archwire slot. While the illustrated slot is rectangular and is designed specifically for reception of complementary rectangular archwires, it is to be understood that the slot can be configured as a cylinder or other cross-sectional shape in the manner presently known with respect to orthodontic bracket design. In use, the slot is partially or completely filled by the cross-sectional configuration of one or more archwires 4 located within it.
As shown, the tie wings 2 are integrally joined within the structure of bracket 1. An intermediate wall section 8 extending across the tie wings 2 in the bracket 1 includes first and second wall sections transversely joining the twin upright tie wings at positions superior and inferior to the archwire slot 20, respectively. Each of the first and second walls includes a surface spaced from one another and flush with the previously-described side surfaces 5, 6 along the archwire slot. The intermediate wall section 8 further includes a surface flush with the previously-described base slot surfaces 7 to provide a continuous archwire slot across the full width of the illustrated bracket 1.
The intermediate wall section 8 serves as a structural boundary surrounding three sides of the archwire slot 20 in the space located between the tie wings 2. In combination with the closed ligating slide 9, it forms a continuous tube across the width of the bracket for reception and capture of an archwire.
A closure complementary to the archwire slot is also provided on the illustrated bracket 1. It takes the form of a ligating slide 9 that is generally planar. The ligating slide movably engages the anterior surfaces of the second tie wing extensions. According to this disclosure, the ligating slide 9 is supported for motion relative to bracket 1 only along the second extensions of the tie wings 2. The anterior portion of second extension of each tie wing 2 includes a guide 9 having an upright inwardly facing guide slot 12. Each guide slot 12 is located anteriorly from the second anterior surfaces.
When the ligating slide 9 is in its open position, the intersection formed between its posterior surface and its open edge is juxtaposed to the corner of side slot surface 6. In this condition, the contiguous corners of the side slot surface 6 and slide 9 provide uninterrupted access to the interior of archwire slot 20. As can be seen in FIGS. 1A and 1B, the cantilevered support for the ligating slide 9 assures a user of an unobstructed oblique view of the archwire slot 20 when looking toward the mouth of one wearing the brackets. This is true whether the bracket is mounted on a lower tooth or an upper tooth. A clinician can therefore readily observe the position of an archwire 4 relative to the boundaries of the archwire slot 20 before closing the ligating slide 9. To assure full width visual and physical access to the archwire slot 20, the open edge of the ligating slide 9 is preferably flush with the inferior side slot surface 6 when the ligating slide 9 is in its retracted or open position.
The anterior surface of ligating slide 9 has a pair of protruding stops at its sides and adjacent to its open edge. The stops are designed to abut the ends of the walls so as to limit the opening movement of the ligating slide 9 relative to the bracket 1. Ligating slide 9 is essentially planar and rigid. However, it is desirable to reinforce its strength by the addition of one or more transverse enlarged ribs.
Looking next at FIGS. 2A-C, shown is another known self ligating orthodontic bracket. FIG. 2A shows a view from the mesial of a prior art bracket 34, shown with a rectangular cross section arch wire 24 of maximum transverse cross section dimensions in the arch wire slot 26. As shown, in order to protect the spring member labial arm portion 28 against excessive labial movement under the action of the arch wire, the prior art bracket 34 has been provided in the arch wire slot gingival surface with a slot 22 extending from the mesial surface to the distal surface and opening to both of those surfaces, into which slot the end of the spring member labial arm portion 28 can extend when in the slot closed position. The slot 22 must be of substantial labial lingual dimension to permit ready insertion of the spring member 30 end therein while the arch wire 24 is displaced out of the slot 26, and to permit the spring member 30 to still engage the arch wire 24 when it is fully inserted in the slot 26. As seen in FIG. 2A, the most usual result is that the presence of the slot reduces the labial lingual dimension of the arch wire slot gingival face 32 to substantially less than the corresponding dimension of the arch wire gingival surface, particularly when the arch wire is of the largest transverse cross section dimensions that can be accommodated in the slot, with the attendant disadvantages discussed above.
FIG. 2B shows a perspective view from the mesial and labial of a prior art bracket, showing in broken lines the ligating latch spring member in slot closed position, while FIG. 2C shows a cross section in a gingival occlusal plane through the prior art bracket of FIG. 2B, showing in solid lines an arch wire of rectangular transverse cross section in the arch wire slot and the corresponding position of the spring member labial portion, showing in broken lines an arch wire of circular transverse cross section in the arch wire slot and the corresponding position of the spring member labial portion, and illustrating the manner in which an opening tool is used in conjunction therewith.
In the brackets 34 of the invention the gingival surface 32 is instead provided with a mesially distally extending retaining recess 36 of smaller mesial distal width than the gingival surface, so that it is closed at its mesial and distal ends and thereby provides labial lingual extending gingival rail surfaces 38 (colloquially referred to as torquing rails) at the closed mesial and distal ends, these rail surfaces being engagable by the arch wire 24 gingival surface over the full labial lingual extent thereof for maximum application of torque moment from the arch wire 24 to the bracket 34. In the embodiments of FIGS. 2A-C the width dimension of the entire spring member 30 in the mesial distal direction is smaller than that of the slot gingival surface 32, and in particular sufficiently smaller than the mesial distal width of the retaining recess 36 that the free end part of the labial portion can be inserted into the recess when the spring member 30 is in the slot closed position, thereby protecting it against excessive labial movement. The labial lingual dimension of the retainer recess 36 is such that the spring member 30 is able to engage the smallest cross-section arch wire 24 with which the bracket 34 is to be used, and is also able to accommodate the largest cross section wire that is to be used with a small amount of clearance between it and the wire when mesial distal movement along the arch wire is required. The maximum extent of the labial movement that is permitted by the recess 36 is well within the amount that would result in over-stressing and damage to the spring retainer member 30, even when the member is of stainless steel and not of one of the shape memory metal alloys.
Accordingly, there is a need for an improved orthodontic bracket wherein an orthodontic wire is held in an open channel or slot which receives an orthodontic wire without means of any type of applied ligature or any type of moving cover. More particularly, there is a need for an improved static self-ligating orthodontic bracket.